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Cell Biology

5 lectures + background reading (Campbell)

  1. Cell structure (chapter 6)
  2. Cell membranes (chapter 7)
  3. Cell division (chapter 12)
  4. Respiration (chapter 9)
  5. Photosynthesis (chapter 10)

Cell membranes

  • Crucial structures of cells
  • Makes a cell a cell!
  • Also called a plasma membrane
  • Fluid mosaics of lipids and proteins
  • Most abundant lipids are phospholipids

Plasma membrane

Phospholipid bilayer

  • Phospholipids have hydrophilic heads and hydrophobic tails
  • Forms a stable two layer membrane between aqueous compartments
  • The hydrophobic tails are “shielded” from the water

What does detergent do?

Phospholipase A2

Membranes are fluid

  • Membranes are dynamic!
  • Phospholipids switch places laterally 107 times per second
  • Some proteins also move around (others attached to plasma membrane)
  • Fluidity changes with temperature

Challenge of hibernation

Challenge of hibernation

Arctic waters

Arctic waters

Membrane synthesis

  • Synthesised in ER
  • Membranes have distinct sidedness
  • Cytoplasmic and extracellular faces

Membrane proteins

  • Determine most of the membrane function
  • Can be:
    • Integral, embedded in the membrane (including transmembrane)
    • Peripheral, loosely bound to membrane surface

Integral membrane proteins

  • Diagram shows transmembrane protein
  • Internal hydrophobic region, contains α helices
  • Hydrophilic regions either side of membrane
  • Can be held in place by cytoskeleton

Protein function

Protein function

Protein function

Protein function

Protein function

Protein function

Membrane permeability

  • Membranes are selectively permeable
  • Constant flow of molecules and ions
  • Examples:
    • In: nutrients, O2, inorganic ions
    • Out: waste, CO2, inorganic ions
  • Molecules passively move through lipid bilayer with varying difficulty
  • Membrane proteins also allow specific molecules to pass through

Passive transport

  • Solutes diffuse across membranes when there is a difference in concentration
  • This requires no energy
  • Move towards equilibrium (equal) concentration either side of membrane
  • E.g. O2 transport into cells

Passive transport using proteins

Osmosis

  • Membranes that are selectively permeable produce interesting effects
  • If a solute cannot move along a concentration gradient, water moves instead
  • Water exchange allows equilibrium
  • BUT water balance is extremely important for cells!

Osmosis

Osmosis

Marine animals in freshwater?

Anadromous fish

Active transport

  • Sometimes cells need a different concentration of solutes inside
  • This requires active pumping of solutes in/out of the cell, against their concentration gradient
  • Requires energy in the form of ATP

Sodium-potassium pump

Membrane potential

Active transport allows electrical charge to be maintained across the membrane

Bulk transport

  • Some items are too big for transport through the membrane
  • Require packaging in vesicles
  • Exocytosis out
  • Endocytosis in

Bulk transport

Bulk transport

Cell Biology

5 lectures + background reading (Campbell)

  1. Cell structure (chapter 6)
  2. Cell membranes (chapter 7)
  3. Cell division (chapter 12)
  4. Respiration (chapter 9)
  5. Photosynthesis (chapter 10)

Next time: Cell Division